1. Field of the Invention
This invention relates to a flexible tube and its manufacturing method, especially, a flexible tube for construction of endoscopes, catheters, guide wires, and artificial blood vessels, and manufacturing method for the same.
2. Description of the Related Art
In these days, apparatuses such as endoscopes, catheters, guide wires are used frequently to be inserted to blood vessels and intestines for examination and operation of human bodies. Each of these apparatuses has a distal portion which bends corresponding to configuration of the blood vessels and the intestines on its end portion or entire body for smooth insertion to the blood vessels and the intestines. Generally, the distal portion is composed of a flexible tube.
The apparatuses such as endoscopes, catheters, and guide wires contact inner portions of the blood vessels and the intestines. For this reason, the flexible tube of which these apparatuses are composed is required to bend smoothly (to be excellent in flexibility). And, wall of the tube is required to be thin to make the outer diameter of the apparatus as small as possible. To fulfill these requirements, conventionally, a rubber tube of thin wall formed by extruding method, a braided metal wire tube composed of a synthetic resin tube covered with metal wires etc. are used as the flexible tube.
And, Japanese life style has been westernized recently, and diseases related to arteriosclerosis have been increasing. Therefore, the demand for artificial blood vessel is becoming stronger year after year. Generally, material for artificial blood vessel is required to have physical and chemical stability in vivo, safety, appropriate anti-thrombotic character, anti-fatigue strength, elastic extensionality similar to that of living organism. And, after the artificial blood vessel is embedded in living organism, a tissue similar to vascular wall is generated on an inner face of the artificial blood vessel. Therefore, it is preferable that the material for artificial blood vessel is effective for forming endoderm cells and regeneration of vascular tissue.
Currently, polyester artificial blood vessels and Teflon artificial blood vessels are applied clinically. The polyester artificial blood vessel is made by that synthetic fibers obtained by melt spinning of polyethylene terephthalate are braided in a tube. And, the Teflon artificial blood vessel is made by that a tube made of polytetrafluoret hylene is extended under certain conditions to fibrilate (microfiberize) the wall construction of the tube.
However, when applied to the flexible tube used for the distal portion mentioned above, although the rubber tube is excellent in flexibility, buckling and twist (kink) are easily generated, and the tube is breakable when it is bent. On the contrary, the above-mentioned braided metal wire tube has advantages that the buckling and the twist are hardly generated and the tube is not breakable, and disadvantages that flexibility is not sufficient and the tube is difficult to be made small in diameter and thin in wall thickness.
On the other hand, a bellows tube is known to solve these disadvantages. The bellows tube has a construction in which a metal coil is embedded in a tube wall formed with resin, and the disadvantages above is to be solved by the construction. Normally, the bellows tube is made by a dipping method in which a metal coil is dipped in melted resin and drawn out of the resin to be a tube, and a taping method in which resin tapes are wound around a coil or disposed in a longitudinal direction on the coil.
The coil is exposed inside the tube in the tube made by the taping method.
However, in the dipping method described above, wall thickness of the bellows tube is difficult to be uniform and thin. Further, in the taping method described above, it is difficult to wind or dispose the tape when the outer diameter of the coil is small. Therefore, it is very difficult to make a bellows tube having outer diameter less than several millimeters conventionally.
And, in the artificial blood vessel described above, the polyester artificial blood vessel and the Teflon artificial blood vessel have problems that crimp (kinking) is generated when the blood vessel is bent and the buckling tends to be generated. These problems are expected to become more serious when the artificial blood vessels will be used as substitute for small blood vessels excluding aorta in the near future.
It is therefore an object of the present invention to provide a flexible tube especially used for endoscopes and artificial blood vessels having excellent mechanical characteristics restricting the crimp phenomenon and buckling in bending, small diameter, and thin tube wall, and a manufacturing method for the flexible tube.